Watching the video several times, I realized that you actually don't know what you're doing either. You made this video hoping to attract views, in reality you don't even know. You mix things up and your explanation is a mess.
I think that all those who want to show how to do the manual calculation for bitcoin, show quickly and without all the explanations, so that people don't understand. You don't want everyone to find out how it's done, so you just pretend to explain, in reality you want it to remain a secret. That's why you don't explain properly and speed up so that nothing is seen.
Just so you know: the autor of this video deleted my posts automaticaly. Those video is a copy of a 2013 video, from @KenShiriff " Mining Bitcoin with pencil and paper"
